I’m a residential GC. I built a master bedroom/bath bump out on 2×10’s on 16″ centers, 8′ lengths. Very solid. Sub-floor is 3/4″ osb/t&g, glued and stapled. We are planning 12″ travertine tile floors over radiant heat cables. One sub suggested 3/8 Hardie board over the sub-floor, then the cable with another 3/8″ of troweled mortar, then the tile using a 3/8″ notch.

I usually mesh tape and coat the sub-floor seams, then lay the cable and fill with a solid 3/8″ pour of leveling compound. Then lay the tile. The 3/8″ Hardie board and hand troweling another 3/8″ seems like a waste of time and money, and adds too much height for a comfortable transition to the next room.

Thanks ronW. Just to clarify, I tape and mud the seams in the osb, then I pour 3/8″ of leveling compound on top of the osb (which also fills in and covers the cables), leaving a 3/8″ layer between osb and tile. Do you think the Hardie is also necessary? Thanks again.

Thanks ronW. Just to clarify, I tape and mud the seams in the osb, then I pour 3/8″ of leveling compound on top of the osb (which also fills in and covers the cables), leaving a 3/8″ layer between osb and tile. Do you think the Hardie is also necessary? Thanks again.

I cant say on that one. Never done it that way. But I’m not a tile expert.
Maybe @chadm or @masterbosch can help out a little more. They both do way more tile work than I do.

Hi guys happy weekend @Rona @category just to be on the same side what you use to bond the mesh to the floor. Do you just mesh the whole floor..?I would use some kind of bedding like @ronw says with out it heated floor is gonna have to much heat change on the osb subfloor. Which may move the flooriing. Probibly will be okey but if you didn’t do it just use bedding… I know floor maybe higher sure which usually happens with the tile. Don’t use quicklevel right on top of osb with out some type of mesh.but what you can do is use wire or plastic mesh put a skim coat like 3/16 then run your wires your floor will be much more solid.

No problem. I would do it like that myself you still gonna end up with max 1/2 for the bedding. I don’t know how level is the floor but if it’s level you may get away with 7/8 finish product. What you also can do is prime the flooring. Before the wire mesh. Then you can run your heat wires then pour. That will work also. But keep in mind that if you using metal wire mesh it may damage your wires if someone walks on it before the quicklevel pour. If you have any question I would try to help much as I can @chattarov

We quite regularly put the cables right on the OSB then do the self leveling for our underpayment. The last job we did with heat on OSB we used Schauter Ditra heat or a similar product. I really liked that system and it does not create the extra height that you are trying to avoid

I have installed the heat wires directly over plywood subfloor on multiple occasions without any issues. Like Kurt said – the Schluter Ditra heat is the way to go…I have used it on 3 projects now and I am a big fan.

I have done a few, usually right on plywood, usually use 1/2 inch sub floor with another 1/2 opposite pattern. Or 3/4 then either ditra or 3/8 ply.
Then the self level cement to cover the cable. It’s been more than 5 to 6 years and never had any issues, , one was comfort , that’s the wire spaced further than regular for heating. and the other few were for actual heating the area.

I know lot of people go right over the subfloor with wires or ditra.. but we have to keep in mind these are wood structures. Moisture and heat levels effects the plywood and there is expansion. Yes I see people use ditra with only thinset under it will it work yes it will. Will I take the chance with it on wood structure not really…

Many thanks to each of you! All very good points. When I ask a hurried question I inevitably leave out some detail so I’ll fill in the blanks. A really solid sub-floor is essential. I use long, wide crown, ring shank staples – they hold through an earthquake. I use them on the Hardie too if I’m using 3×5’s

I waterproof everything heavily. Then lay a plastic mesh cloth over it all, applying mud over that at all the osb seams. Then the cables. Then I screw stainless steel screws through the mesh into the osb leaving them 1/4″ high, and then pour the leveling compound. This way you have essentially created one solid Hardie board with integral mesh that is actually screwed down.

All of your ideas and experience are really helpful and appreciated. Thanks to each of you! And Blessed Holidays to all.

I had a big , self leveled floor with heat wire fail during install once, it cracked like crazy . We likely mixed it too thin.

The new mats are a dream, you can lift the wire and reroute it until you get the placement just where you want it, then you just trowel the thinset in . Once I used one , I decided I’d likely never try to embed one again .

I personally have not installed any. I have hooked it up. Usually the tile guys already have it in and I fish the leads to the tstat and run the power and make the connection. Sorry I could not be of more help.